The field of the invention pertains to semi-truck trailers and, in particular, to curtain side trailers adapted to general cargo and palletized cargo.
Typical curtainside semi-truck trailers comprise a floor supported by a pair of longitudinal girders extending the full length of the trailer. The girders are commonly of I-section with the web depth varying in accordance with floor support requirements. At the forward end of the trailer, the king pin for the fifth wheel may be supported in a monocoque assembly. The monocoque assembly and I-section girders extending into the assembly are typically seven or more inches in depth. The minimum depth has been limited by the need for sufficient strength and moment of inertia in the girders to support the trailer floor and cargo. Attempts to reduce below seven inches the web depth of the I-section leading through the gooseneck into the monocoque over the fifth wheel have not been fully successful for full size semi-trailers because of excessive flexing and twisting under load.
Since the outside height of a semi-truck trailer is limited, each inch of clearance between the roof and floor is important to maximize cargo capacity. For a full size trailer about eighty cubic feet of cargo space can be gained for each inch of increased roof to floor distance.
The overall width of a semi-truck trailer is also limited, therefore the rear door opening is also limited by the necessary thickness of the rear corner posts of the trailer. In a rear door curtain side trailer the rear corner post column stability is solely dependent on the column itself because there is no adjoining sidewall or end wall to reinforce the column. Typically, the column is two inches or more in thickness and seven or more inches wide toward the front of the trailer.